Classical trajectories are used to calculate reactive cross sections vs. translational and vibrational energy for hydrogen atom addition to ethylene to form the vibrationally excited ethyl radical. Exciting the C=C stetch and CH2 wagging motions of ethylene has only a minor effect on the reactive cross section. Variations in the potential energy surface were investigated. Narrowing the angular width of the H + C2H4 → C2H5z.ast; entrance channel decreases the reactive cross section at low translational energies, but increases it at high translational energies. The classical trajectory threshold for C2H5* formation is found to be similar to the zero point vibrationally adiabatic barrier. Neither removing zero point energy from ethylene or replacing the attacking atom with deuterium causes major changes in the reactive cross section. The reactive cross sections vs. translational energy for hydrogen atom addition to ethylene are compared with those for the model reaction H + C=C → HCC*.